Around 1:50 p.m., a Vallejo city employee got a call warning that a bomb was set to detonate at the building sometime this afternoon, Deputy Daryl Snedeker said.
That prompted the evacuation of more than 100 people -- including judges, lawyers, bailiffs and members of the public -- around 2 p.m., he said.
In a sweep of the courthouse and the surrounding grounds, deputies found only an unattended makeup bag in an overflow court parking lot, he said.
A court employee did find a small zippered bag in a plant in the overflow parking lot.
The package was deemed suspicious and that area was evacuated and access was restricted by deputies, Snedeker said.
Snedeker said that a sheriff's K-9 unit and an explosives team from Travis Air Force Base conducted an extensive secondary search of the interior and exterior of the courthouse but did not locate any explosives.
Napa County sheriff's crews also responded to the area and used its bomb robot and x-rayed the suspicious package, he said.
The crew determined the package was an old first-aid kid with several items including an old, rusty firearm that did not appear to be operational, Snedeker said.
The firearm was seized by Solano County sheriff's deputies and booked into evidence.
The courthouse was opened up just after 6:30 p.m., he said. Court proceedings were suspended for the day and will resume today.